Fate of PAHs in the post-combustion zone: Partial oxidation of PAHs to dibenzofuran over CuO

The main objective of this work is to investigate how different polycyclic aromatic hydrocarbons (PAHs) will react over a catalyst under post-combustion zone conditions. It is important to know if PAHs polymerize/condense on the catalyst surface to form carbonaceous material (coke) or if they partially oxidize to form dibenzofuran or similar structures. Also, the formation of dibenzofuran from different PAHs studied in this work should help clarify the role of PAHs in the formation of an important class of pollutants like polychlorinated dibenzofurans (PCDFs). In this work, the transformation of seven different PAHs were studied over a CuO catalyst at temperatures between 250 and 350 degrees C in 10% oxygen. All experiments were conducted in a fixed bed flow reactor system with an on-line GC/MS, which trapped and analyzed gaseous reaction products. The results of this study show that when the four or higher ringed PAHs are passed over CuO catalyst under post-combustion zone conditions, they are primarily converted to coke, but the lower ringed (two or three rings) PAHs are partially oxidized. The results of this study show that the decomposition of PAHs to lower aromatic compounds can follow two different pathways: one where anthracene is an intermediate and other where phenanthrene is the intermediate. However, dibenzofuran, an important product, is only formed in the phenanthrene pathway. Further investigation showed that in the phenanthrene pathway, dibenzofuran can directly form from fluorenone, biphenyl and fluorene and that the concentration of these three PAHs can be used to predict dibenzofuran yields. (C) 2005 Elsevier B.V. All rights reserved.